Harrison responded by planning an appeal and laughing off the suspension. "Lol!" he tweeted, later telling a reporter: "If I would have really hit him, I would have close to knocked him out."

Some former players offered support, with Deion Sanders, now a commentator for NFL Network, saying: “C’mon guys, this is football.”

But the suspension is further evidence that the NFL has turned a corner and is now siding more with medical professionals than with the game's gritty past.

“This is consistent with the new, low-tolerance policy of the NFL alongside the growing research showing the long-term effects of concussions,” says Dave Czesniuk, director of operations for Sport in Society at Northeastern University in Boston.

The NFL’s official statement noted that Harrison has been the league's biggest repeat offender. "In addition to four fines for illegal hits against quarterbacks in 2009 and 2010, Harrison also was fined twice for unnecessary roughness during that period. Harrison totaled six fines in that two-year period."

While Harrison has vilified Commissioner Roger Goodell over the new initiative and has vowed never to change his style, his appeals are coming up against a mounting body of medical research that points to the dangers of repeated head injuries.

“Fans need to understand that these players are putting themselves at risk not only during each game, but cumulatively over time in ways that don’t necessarily show up until after retirement,” says Ricardo Komotar, an assistant professor of clinical neurosurgery at the University of Miami in Florida.

Even past players known for their physical style have spoken about the need to protect players form head shots.

"When you definitely go for someone's head when they're not looking, I don't know if I agree with that," said former Chicago Bears linebacker Dick Butkus in an ESPN.com chat. "They're trying to make this game a little safer, and I think the QB should be protected."

Some observers hope the suspension will send a signal from the NFL all the way through college, high-school, and little league football.

“From an ethical perspective, America needs to debate the cost of these kinds of injuries in both the short and long term," adds Brett Wilmot, an ethics professor at Villanova University in Pennsylvania. "People getting hurt and incapacitated over time for what is essentially entertainment and a pastime is not something that should be taken lightly.”

Mr. Czesniuk of Sport in Society suggests that the suspension might have an effect.

“This has gotten a lot of attention and because I don’t think [Harrison’s] intent was malicious or distasteful, the suspension will likely cause other players to tiptoe a little bit more around making similar-type hits,” he says.